1. Field of the Invention
The present invention relates to an ink-jet recording method and an ink-jet recording apparatus, and more precisely relates to an ink-jet recording method and an ink-jet recording apparatus for recording by forming an ink image on an intermediate transfer body, and transferring the ink image to an recording medium.
2. Description of the Related Art
The ink-jet recording system, electrophotographic system, thermal head system, dot impact system and the like are currently utilized as recording systems for image recording apparatuses that record and output in response to the request of users the images made by computers, duplicate images of printed matters, and facsimile images.
Among the systems, the ink-jet recording system is a quiet printing system that prints letters and images by directly ejecting the ink onto materials for printing (recording media) such as paper, cloth, plastic sheets, etc. in response to image signals. Since this system does not require any complicated apparatus, its running cost is low and it is easily downsized and colorized. The system is further variously advantageous, for example, in flexibility towards size of recording media from card size to large poster size. In terms of quality of images also, output of images with quality as high as that of silver salt color photographs has become possible in recent years. Since recording apparatuses utilizing the ink-jet system are advantageous as described above, they are used not only for printers as output apparatuses connected to personal computers but also as output apparatuses for office automation machines such as facsimiles and copy machines. Further, the systems are also widely used in the field of industrial production for printing various cards, packages and large-size posters.
As a recent trend in various fields, there is a demand for outputting high quality images by means of ink-jet recording system regardless of kinds of recording media. In order to meet such a demand, especially in these cases, factors or phenomena such as “feathering”, “beading”, and “bleeding” that cause deterioration of images on recording media as described later need to be controlled. These phenomena have become more pronounced as ink-jet recording becomes faster.
The above-mentioned phenomena that cause deterioration of images are closely related with characteristics of recording media and properties of inks for recording. In the case of forming images on recording media formed with cellulosic fiber, such as regular paper (PPC), by ejecting inks, for example, “feathering” phenomenon or exudation of ink along the fiber comprising the recording media unless the inks or the recording media are provided with any chemical treatment. In the case of forming images on non-absorbing recording media comprised of plastic sheets such as PET (polyethylene terephthalate) and polyethylene that reject infiltration of solvents, or on gloss printing paper that allow only a little infiltration of inks, a phenomenon called “repelling” occurs in which inks ejected onto the recording media are not completely absorbed and flow. At the same time, the ink dots that are formed on the recording media gather together and neighboring ink dots get mixed, resulting in the phenomenon of “beading”. Further, overlapped colors exude to each other at their boundary, resulting in the phenomenon of “bleeding” and deterioration of quality of image formation. Therefore, it has been difficult to form good images on regular paper or non-absorbing recording media by means of an ink-jet recording system.
As the method for solving the above-mentioned problems, ink-jet recording using inks that are made to fit various recording media by changing solvents in ink compositions or causing liquid-solid phase changes is known. Here, the main solvents of recording inks are classified as oil-based, organic solvent-based and water-based solvents. Generally, when oil-based and organic solvent-based inks are used, the apparatuses need to be provided with exhaust and recovery systems to avoid odor and influence to environment and human bodies, resulting in the problem that the apparatuses become larger. Further, rapid evaporation of the solvents tends to cause clogging of nozzles of the print head which are ejection port. Therefore, it is not advantageous to use oil-based and organic solvent-based inks for recording. Water-based inks, on the other hand, do not require consideration of influence to environment and human bodies in conformation of apparatuses, since tasteless, odorless, and colorless water is used as the solvent. Also, water-based inks are free from clogging of nozzles by inks and are widely used.
There is a recording system called a hot melt ink-jet system that utilizes liquid-solid phase change. When this system is used, the inks are heated to become less viscous and either ejected directly onto recording media or ejected onto heated intermediate transfer body for formation of ink images. The ink images are then transferred from the transfer body to recording media to form images. In either case, the inks are solidified by spontaneous cooling on recording media to form images. Such a hot melt system has an advantage that recording on any recording media is possible.
This system, however, requires exertion of liquid-solid phase change characteristics of inks. This results in increase in amounts of resin which shows liquid-solid phase change characteristics much more than colorants, and requires large amount of inks on recording media in order to obtain desired optical concentration. As a result, there has been a problem of deterioration of quality of images due to thickness of inks deposited on the recording media. Further, since solid inks need to be once melted to make liquid, it is necessary to keep the ink supply routes and print heads heated during operation of the apparatus and to always maintain the ink onto liquid states, causing consumption of enormous amount of energy. The system is not useful from the view point of energy saving either.
Many of other known recording systems that intend to solve the above-mentioned problems propose so-called transfer systems that once form ink images on an intermediate transfer body by means of an ink-jet recording system, increase the viscosity of the ink images on the intermediate transfer body through drying of the ink or remove of the solvent from the ink images to concentrate the ink, and then transfer the ink images from the intermediate transfer body to the recording media (U.S. Pat. No. 4,538,156, U.S. Pat. No. 5,099,256, and Japanese Patent Application Laid-open No. 62-092849(1987)). The recording methods of these transfer systems are not methods of forming images on recording media through infiltration of water in the ink into the recording media as in the conventional ink-jet recording systems. Therefore, they are effective means especially for preventing feathering phenomenon in which inks spread along fibers of a recording media while the inks infiltrate into the recording media. Further, it is possible to control amounts of water and solvents of the inks for forming ink images on the intermediate transfer body, and control its viscosity in accordance with an ink infiltration characteristic when the ink images formed are transferred from the intermediate transfer body to recording media. Thus, flexibility of usable recording media is increased. Further, use of an intermediate transfer body in ink-jet recording separates the print head having the nozzles for ejecting inks from the recording media. Therefore, there are various advantages such as preventing clogging of the print head through deposition of paper powder from recording media on the nozzles.
In order to obtain higher quality images by means of ink-jet recording systems utilizing an intermediate transfer body, however, it is desirable to satisfy the conditions described in the following [1] through [4].
[1] The ink images on the intermediate transfer body are formed as images without beading and bleeding.
[2] The ink images formed on the intermediate transfer body is transferred to the recording media without deterioration of the images.
[3] The transferred ink images are free from offset when dried, fixed and piled, and have abrasion resistance.
[4] The intermediate transfer body is easily cleanable after transfer, and able to repeat forming images.
However, the following problems have arisen about the above-mentioned item. Concerning [1], since the intermediate transfer body used is not a recording medium that allow infiltration of ink solvents, beading by which the neighboring ink dots ejected onto the intermediate transfer body stick with one another to unduly diffuse or flow, and positions or shapes of the dots are significantly changed occurs damaging the images. Then, transferred images naturally become damaged so that eventually high quality images cannot be formed on the recording media.
Concerning [2], when the ink images formed on the intermediate transfer body are transferred to the recording media, local failure in transfer of portions of the ink images or generating state in which ink images dissociate inside and the dissociated ink images are transferred the intermediate transfer body and the recording media respectively causes irregulars coloration or optical concentration of the images on the recording media, and good images cannot be formed.
Concerning [3], when the amount of resin is too small in the ratio between colorant and resin that are solid components of ink images transferred to recording media such as printing paper, or when a nonvolatile solvent component other than water, such as organic solvent, remains in ink images even if there is enough amount of resin, cohesive force of the solid components of the inks that form ink images becomes weak. This causes offset ink smear when recording media are piled, or ink smear through abrasion.
Concerning [4], when a large amount of inks forming ink images on the intermediate transfer body remains on the intermediate transfer body after transfer, it gives a tremendous load on cleaning. This not only results in problems such as reduction of recording speed and energy consumption due to cleaning, but also causes problems such as generation of a large amount of waste inks and that apparatuses become larger.
In order to solve the problems, Japanese Patent Application Laid-open No. 5-200999(1993) discloses an apparatus which emits ink dots from an ink-jet print head onto an intermediate transfer body, concentrates the ink by making the intermediate transfer body absorb the solvent in the inks, and transfers the inks to a recording media. The apparatus is one of the useful means that enable formation of good images.
The apparatus disclosed by the Japanese Patent Application Laid-open No. 5-200999(1993), however, has a unique problem that efficiency of transfer to recording media is reduced due to clogging of solvent absorption holes of the intermediate transfer body. It makes the cleaning of residual inks on the intermediate transfer body a big deal. Moreover, there is also a problem of much energy consumption in recovering initial condition of the transfer body by removing the solvent absorbed in the intermediate transfer body by air suction and discharging absorbed water by heating.
Japanese Patent Application Laid-open No. 11-188858(1999) proposes a method and an apparatus that first form powder soluble to or swellable with inks on an intermediate transfer body, form images by emitting ink drops from an ink-jet print head onto the transfer body, and then transfer the images from the intermediate transfer body to recording media.
The method disclosed by the Japanese Patent Application Laid-open No. 11-188858(1999), however, consumes much energy in removal of water taken in by the powder that is capable of absorption of water. When images still containing water are transferred to recording media, the water absorbed by the recording media expands the images, damages sharpness of the images, and reduces optical concentration, causing deterioration of the images. In imageless portions of the intermediate transfer body where no image is formed, there remains uncolored water absorbing resin powder. It may cause stain on the recording media during transfer and further deterioration of the quality of images. The image forming method utilizing the above-mentioned process is useful as a method for fixing images on an intermediate transfer body. In the image forming method, however, in order to stably supply the transfer body with powder again after transfer, a process of recoating powder is required after cleaning of the powder in imageless portions on the transfer body. The apparatuses for cleaning the intermediate transfer body and powder coating take much space.
Japanese Patent Application Laid-open No. 1-146750(1989), on the other hand, discloses an apparatus that forms a thin film of glycerin capable of releasing oil-based inks on an intermediate transfer body, whereon ink images are formed with oil-based inks. Thus, use of oil-based inks as inks for forming images on recording media enables formation of good ink images on the intermediate transfer body.
The apparatus disclosed by the Japanese Patent Application Laid-open No. 1-146750(1989) can provide images with high quality and good water resistance when oil-based inks are used as described above. The oil-based inks described above, however, may adversely influence human bodies and environment, since they contain organic solvents that are harmful to human bodies and environment. When the method is carried out using water-based ink compositions taking influence on human bodies and environment into consideration, beading and bleeding occur due to good affinity of the water-based inks with the glycerin film formed on the intermediate transfer body, and images formed are distorted. There is another problem that rapid fixing is impossible due to slow drying.
Further, Japanese Patent Application Laid-open Nos. 7-089067(1995) and 7-256873(1995) disclose methods for carrying out ink-jet recording by coating surfactants in advance on an intermediate transfer body with releasing property to provide it with increased wettability for water-based inks. These methods solve the problem of exudation of inks on recording media by forming images with water-based inks on an intermediate transfer body which is coated with a surfactant in advance, and transferring them to recording media when appropriate viscosity is attained.
The methods for solving problems in ink-jet recording using an intermediate transfer body disclosed by the Japanese Patent Application Laid-open Nos. 7-089067(1995) and 7-256873(1995) are useful when images are formed on an intermediate transfer body or recording media using an ink of a single color, such as a black ink of same concentration, alone. They are not decisive solutions, however, in case colored high quality images are formed by ejecting inks with different concentrations and colors from plurality of different nozzles onto predetermined image address points on recording media.
It is clear as described above that there still remain problems to be improved, although various methods have been proposed for carrying out formation of good images on regular paper and non-absorbing recording media, when image formation is carried out by means of an ink-jet recording system utilizing an intermediate transfer body. In particular, a demand for rear face printing of a printed sheet immediately after rapid record output, or a demand for implementation of book binding, namely cutting and folding, of recording media immediately after output have been raised. Therefore, further improvement is required in rapid drying and fixing of ink images transferred from an intermediate transfer body to recording media, and in complete fixing with good abrasion resistance.
In order to solve such problems, methods of increasing materials for reducing flowability of color inks (also called “image fixing components” in this specification) and the amount of such additives as high molecular weight resins in inks can be considered. Excessive addition of additives to inks, however, has been possible to cause deterioration of stability of ink discharge from an ink-jet print head, and reduction of stability of means of coating due to retention of resin in the means of coating due to drying of image fixing components.